Compliant mandrel and mandrel assembly for growing graft tubes

ABSTRACT

A mandrel of sponge rubber or gel has a tension element for withdrawing the mandrel from a graft tube grown from living tissue. In a first embodiment the tension element comprises a strip of cloth embedded in a sponge rubber mandrel. In a second embodiment the tension element comprises a rubber tube containing the sponge rubber and in a third embodiment the tension element comprises a rubber tube containing a gel. The mandrel assembly includes cloth reinforcing tubes surrounding the mandrel.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of my co-pending applicationSer. No. 368,811 filed June 11, 1973, on Apparatus for Growing GraftTubes in Place, now U.S. Pat. No. 3,866,609; which is a continuation ofmy application Ser. No. 241,189 filed Apr. 5, 1972 on Apparatus forGrowing Graft Tubes in Place, now abandoned; which is a division of myapplication Ser. No. 101,031 filed Dec. 23, 1970 on Method and Apparatusfor Growing Graft Tubes in Place, now U.S. Pat. No. 3,710,777.

BACKGROUND OF THE INVENTION

This invention relates to an improved mandrel and mandrel assembly forgrowing graft tubes of living tissue and to a method for making themandrel.

In the related applications identified above, which are herebyincorporated by reference, a mandrel assembly having a pair of clothtubes on a flexible silicone rubber mandrel is implanted in a livingbody to grow a graft tube in the place where it is to be used or to growa transplantable graft tube which may be autogenous, homologous, orheterologous. Such graft tubes may be used as arteries, veins,esophagus, ureters, bile ducts, or trachea.

The mandrel assembly disclosed in said related applications has beenused successfully for a considerable period of time by skilled surgeons.When the mandrel assembly is implanted in a living body, connectivetissue from the body grows through the double layers of the cloth tothoroughly encapsulate the cloth and fill both an inner space betweenthe inner cloth layer and the mandrel and an intermediate concentricannular space between the two layers of cloth.

The inner layer of cloth serves primarily as a spacer element to holdthe outer layer of cloth away from the mandrel, and the filling of theinner and intermediate spaces just mentioned assists in this purpose.Thus, the outer layer of cloth provides a primary reinforcement tostrengthen the graft tube adjacent its outer surface where reinforcementis most effective. The inner cloth tube also provides additional orsecondary reinforcement, the two layers of cloth thereby greatlystrengthening the wall of natural body tissue.

When the graft is grown in situ, or the place where it is to be used,the graft tube is completely vascularized and is a living part of thebody when the ingrowth of tissue is complete and the mandrel withdrawn,leaving a lumen in the tube. The ends of the graft tube are thenanastomosed to the tube or tubes of the body which the graft tube is toserve.

When the graft tube is to be transplanted to another location in thesame body, or to a different body, it is similarly completelyvascularized during its period of growth but upon transplant it mustestablish a new blood supply system and when the new blood supply isestablished, the graft becomes a living part of the body in which it isimplanted.

The objects of the present invention are to provide an improved mandreland mandrel assembly for growing a graft tube, to provide a mandrel andmandrel assembly which do not require as much skill on the the part ofthe surgeon, to provide a mandrel and mandrel assembly which will moreconsistently grow graft tubes of uniform quality, to provide a morecompliant mandrel, and to provide a method for making a compliantmandrel.

SUMMARY OF THE INVENTION

The task of the surgeon is made less difficult and exacting by using amore compliant mandrel to form the lumen. A more compliant mandrel alsoprovides greater flexibility for growing graft tubes for the differentpurposes mentioned above. In one form of construction a compliantmandrel is made of foam or sponge rubber which has a relatively soft andyielding texture. Since foam rubber is deficient in tension, a separatetension element may be incorporated in the mandrel in order to withdrawthe mandrel from the graft tube when the growth of the graft tube iscompleted. This tension element may be a strip of cloth molded into themandrel. A method for making such a mandrel is described in detail.

Other embodiments of compliant mandrel comprise a thin tube of siliconerubber filled with sponge rubber or silicone jelly. In such cases thesilicone rubber tube provides the tension element for withdrawing themandrel from the completed graft tube.

The invention will be better understood and additional objects andadvantages will become apparent from the following description of thepreferred embodiments illustrated on the accompanying drawing. Variouschanges may be made in the details of construction and in the methods offabrication and certain features may be used without others. All suchmodifications within the scope of the appended claims are included inthe invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmentary perspective view of a mandrel assembly withparts broken away to show a mandrel embodying the invention;

FIG. 2 is a longitudinal sectional view with parts broken awayillustrating the method and apparatus employed in making the mandrel inFIG. 1;

FIG. 3 is a view similar to FIG. 1 showing a modification of themandrel; and

FIG. 4 is a view similar to FIGS. 1 and 3 showing a furthermodification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a mandrel assembly having a compliant cylindrical mandrel10 inserted in an inner cloth tube 11 and an outer cloth tube 12. Thereenforcing tubes 11 and 12 are preferably made of a knitted Dacronmaterial which has been impregnated with a suitable stiffening agentsuch as silicone rubber vulcanized in situ as described in the relatedapplications identified above. Tube 11 has an inside diameter slightlyexceeding the outside diameter of mandrel 10, and tube 12 has an insidediameter slightly exceeding the outside diameter of tube 11.

When this mandrel assembly is implanted in a living body or placed in asuitable culture, living tissue grows through the porous tubes 12 and 11filling the annular space between these tubes and also filling theannular space between tube 11 and mandrel 10 whereby the tubes 11 and 12form reenforcing members for a graft tube of living tissue.

Mandrel 10 has a smooth surface which casts a smooth lumen in the grafttube. The smooth surface on mandrel 10 is also essential for removal ofthe mandrel after the ingrowth of tissue through reenforcing cloth tubes11 and 12 has been completed. After being grown in a living body, theresulting graft tube may be used in the place where it is grown, it maybe transplanted to a different location in the same body, or it may betransplanted to a different living body. When grown in a culture, themandrel 10 is removed and the graft tube implanted where needed in aliving body.

The present invention is concerned essentially with the mandrel per se.Mandrel 10 comprises an elongated cylindrical body of silicone spongerubber 13 having a smooth outer surface. Since the sponge rubber lackssufficient strength, an internal tension element 15 is provided forpulling the mandrel out of the graft tube after the ingrowth of tissuehas been completed. In FIG. 1 the tension element 15 comprises a stripof cloth which is preferably a knitted Dacron tube similar to oridentical to the tube 11 or the tube 12. Cloth element 15, however, isnot impregnated with silicone rubber vulcanized in situ as are tubes 11and 12.

FIG. 2 illustrates the method of making mandrel 10. A casting, moldingof forming tube 20 is suspended in a vertical position. Tube 20 has aninside diameter equal to the desired outside diameter of the spongerubber body 13. The inside surface of tube 20 must be smooth so as tocast a smooth surface on the sponge rubber body. Tube 20 may be made ofTeflon or vinyl plastic or it may be a glass tube coated on the insidewith a suitable release agent. The upper end of tube 20 is fitted with ashort length of rubber or transparent plastic tubing 21 and the lowerend is similarly fitted with a piece of tubing 22.

Knitted Dacron tube 15 is carefully slit longitudinally and one end istied in a knot 23. A weight 24 is attached to this end with a thread 25.Slit cloth tube 15 is lowered through the casting tube 20 until the knot23 is disposed in tube 22 below the lower end of tube 20. Then a pin 26is inserted through tube 22 and knot 23 and adjusted to as to positionthe knot on the center line of tube 20. Weight 24 is cut off andremoved.

When the upper end of cloth 15 which is emergent from the upper end oftube 21 is drawn upward with light tension as indicated by arrow 27, theslit tube is stretched slightly in a longitudinal direction causing itto curl or roll as shown, reducing its diameter. The upper end of cloth15 is thus held carefully under a light tension in a position to placethe cloth as close as possible to the center line of casting tube 20.The reduction in diameter by the curled configuration of cloth tube 15resulting from the upward tension at 27 holds the cloth spaced away fromthe inside wall of tube 20.

A suitable sponge rubber may be made from Silastic No. 386 foamelastomer with catalyst No. 708 (stannous octoate) supplied by DowCorning Company. These materials are mixed and injected under lowpressure into the lower end of tube 22 producing a foaming mixture whichrises up through casting tube 20.

At the same time, the mixture fills and completely impregnates thecurled cloth strip 15, causing this tension member to be integrallyinterlocked with the entire length of the column of sponge rubber whichresults from the setting of the elastomer. The operation must be carriedout so that the gas bubbles generated in the elastomer are small in sizeand completely enclosed by elastomer. The upward injection in the mannerdescribed prevents the inclusion of air bubbles in the elastomer. Duringinjection cloth strip 15 is maintained in the center of casting tube 20.

When the elastomer has set, pin 26 is withdrawn, tubes 21 and 22 areremoved, and the resulting mandrel 10 is pulled out of tube 20. Clothstrip 15 has a degree of longitudinal elasticity characteristic ofknitted fabric which is desirable for the present purpose. When themandrel 10 is to be withdrawn from a graft tube having living tissueencapsulating the reenforcing tubes 11 and 12 and filling the spacebetween tube 11 and the mandrel, a pull exerted on one end of strip 15stretches both strip 15 and sponge rubber body 13 to some extent,elongating the mandrel and slightly contracting its diameter and therebyreleasing the mandrel from the grip of the surrounding tissue.

Also characteristic of knitted fabric, a relatively small amount ofelongation causes the fabric to reach its limit of stretch so that thesponge rubber is not stretched to the point of rupture. The knittedconfiguration of loose loops of thread behaves as a loose chain. Whenthe links are pulled tight on each other there is no further elongationof the fabric and the full tensile strength of the threads is developedfor pulling the mandrel out of the graft tube without over-stressing thesponge rubber in tension.

In the modification in FIG. 3, the mandrel 10a has an external tensionelement 30 comprising a thin walled silicone rubber tube. This tube isfilled with sponge rubber 31 which may be the same silicone spongerubber indicated at 13 in FIg. 1. Tube 30 has a smooth external surfaceto cast a smooth lumen in the living tissue of the graft tube.

In the modification in FIG. 4, the mandrel 10b has an external tensionelement in the form of a silicone rubber tube as in FIG. 3. In this casethe tube 30 is filled with a silicone rubber gel 32. The ends of tube 30are tied with ligatures 33 to retain the gel.

In the mandrel assembly in FIG. 3 the sponge rubber core 31 issignificantly weak in tension. In the mandrel assembly in FIG. 4 the gel32 is substantially without any strength in tension. In each case thetube 30 provides a tension element for withdrawing the mandrel from thegraft tube. When a pulling force is exerted on one end of tube 30, themandrel elongates slightly, producing a contraction of its diameterwhich facilitates withdrawal.

In the related applications referred to, the mandrel is a solid siliconerubber rod having only sufficient flexibility to move with movements ofthe body in which it is implanted as, for example, the movements of theknee and hip joints. Experience indicates, however, that far greaterflexibility is desirable both to simplify the surgery and to accommodateimplantation in other regions of the body in certain cases.

It is also found that in some cases a solid silicone rubber rod has toomuch longitudinal rigidity, causing movements of the ends of the rodwhen the rod is flexed. This impairs the quality and uniformity of thegraft tube and complicates the surgery in order to insure good results.It is desired to have no longitudinal movement of the mandrel underbending.

The present mandrels 10, 10a and 10b avoid these difficulties. Thesemandrels are compliant to the body and substantially limp. This is trueof the tension element in each embodiment as well as the body materialof sponge rubber or gel. Bending does not produce longitudinal movement.Even when the location in the body causes the mandrel to be partiallyflattened, the quality of the graft tube is not impaired. Flatteningdoes not diminish the circumferential dimension and the graft tube isfree to resume circular shape with the full intended cross section areaof the lumen available in use.

In the case of mandrel assemblies for growing tracheal and esophagealgraft tubes, a tension element may not be necessary for pulling a spongerubber mandrel out of the graft tube after the growth of the graft tubeis completed. These graft tubes have much larger diameters and shorterlengths than graft tubes for blood vessels and the sponge rubbermandrels may be readily pushed out of the completed graft tubes.

Having now described my invention and in what manner the same may beused, what I claim as new and desire to protect by Letters Patent is: 1.A mandrel assembly for growing a graft tube with living tissue,comprising an elongated compliant mass of material which may not havesufficient tensile strength for withdrawing the mandrel from saidmandrel assembly after said graft tube has been grown, and a complianttension element extending throughout the length of the mandrel andforming an integral part thereof for pulling the mandrel out of saidmandrel assembly after said graft tube has been grown, an outer fabrictube on said mandrel, and an inner layer of porous material holding saidfabric tube spaced away from said mandrel.
 2. A mandrel assembly asdefined in claim 1, said tension element being disposed within saidcompliant mass of material.
 3. A mandrel assembly as defined in claim 2,said compliant mass of material comprising sponge rubber.
 4. A mandrelassembly as defined in claim 2, said tension element comprising a stripof cloth.
 5. A mandrel assembly as defined in claim 1, said tensionelement comprising a rubber tube containing said compliant mass ofmaterial.
 6. A mandrel assembly as defined in claim 5, said compliantmass of material comprising sponge rubber.
 7. The invention of claim 1,said inner layer of porous material comprising an inner fabric tubewithin said outer fabric tube.
 8. A mandrel for use in a mandrelassembly for growing a graft tube with living tissue, comprising anelongated compliant mass of material which may not have sufficienttensile strength for withdrawing the mandrel from said mandrel assemblyafter said graft tube has been grown, and a compliant tension elementextending throughout the length of the mandrel and forming an integralpart thereof for pulling the mandrel out of said mandrel assembly aftersaid graft tube has been grown, said tension element comprising a stripof cloth disposed within said compliant mass of material, said strip ofcloth comprising a longitudinally slit tube of said cloth.
 9. A mandrelas defined in claim 8, said slit cloth tube comprising a knittedmaterial.
 10. A mandrel for use in a mandrel assembly for growing agraft tube with living tissue, comprising an elongated compliant mass ofmaterial which may not have sufficient tensile strength for withdrawingthe mandrel from said mandrel assembly after said graft tube has beengrown, and a compliant tension element extending throughout the lengthof the mandrel and forming an integral part thereof for pulling themandrel out of said mandrel assembly after said graft tube has beengrown, said tension element comprising a rubber tube containing saidcompliant mass of material, said compliant mass of material comprising agel.
 11. A mandrel assembly for growing a graft tube with living tissue,comprising a sponge rubber mandrel, an inner cloth tube on said mandrelimpregnated with silicone rubber which is vulcanized in the clothleaving the cloth porous, and an outer cloth tube surrounding said innertube and mandrel, said outer tube being impregnated with silicone rubberwhich is vulcanized in the cloth leaving the cloth porous.